I have never trained at Iwama, but I have trained at the Yoshinkan Hombu and understand what you must be going through. Friends of mine who have returned to their home countries after doing some pretty intensive training here have expressed similar sentiments (I still live in Japan).
One of the most useful remarks a teacher of mine made to me as I was complaining about being told to work with beginners was that "You can learn something from everyone". Basically he meant that there is no wasted training..you get out of if what you put into it and you can find something to practice no matter who your partner is. Over the years I have realized how true this is.
Welcome back and as your physical health catches up to your mental Aikido please consider the above. I think it will help...as it does for me